1. Field of Invention
The present invention relates to a display driver IC with a triple-port RAM built therein.
2. Description of Related Art
An IC having a built-in RAM as a display driver IC is known. Furthermore, a triple-port RAM is known as a RAM that is used in the IC with the built-in RAM.
In the triple port RAM, two ports are used to write in and read out data from, for example, an MPU external to the IC. In other words, it is capable of writing data in a certain memory cell through one port, and reading data from another memory cell through another port at the same time. Therefore, this type of RAM requires two word lines and two pairs of bit lines for one memory cell. Furthermore, the remaining one port among the three ports is connected to a line that is exclusively used for reading data from memory cells for display. For this reason, each of the memory cells is also connected to the display word line and the display read line.
In recent years, processes have been developed for manufacturing even more miniaturized semiconductor devices, and memory devices with greater memory capacity have been developed.
An IC with a built-in RAM having many memory cells is manufactured using the miniaturization process, and a liquid crystal display panel is driven by the IC with a built-in RAM.
In some instances, it has been confirmed that data in the RAM are not displayed as they are written. It has been determined that these incidents result from the fact that signals read out through the display read line are interfered with by other wirings and thus deteriorated.
It is an object of the present invention to provide a display driver IC that can drive display elements for display according to data written in memory cells.
It is another object of the present invention to provide a display driver IC that can prevent problems that may result from capacitor coupling between a display read line and two pairs of bit lines.
It is still another object of the present invention to provide a display driver IC that can prevent interference between a display read line and two pairs of bit lines.
A display driver IC in accordance with the present invention includes:
a plurality of memory cells arranged in a column direction;
a plurality of word lines arranged along a row direction, and capable of asynchronously selecting any two of the plurality of memory cells;
two pairs of bit lines extending along the column direction and commonly used by the plurality of memory cells, which are to be connected to selected two of the memory cells;
a plurality of display word lines that successively select the plurality of memory cell along the column direction; and
a display read line extending along the column direction and commonly used by the plurality of memory cells, which is to be connected to one of the memory cells successively selected by the plurality of display word lines, such that, as viewed in a plan view, the display read line is disposed in one of the two pairs of bit lines.